18" or 19"? Advice needed.

Virtually makeing the twisty bits straight

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Oh my yes Matt!. You understand my motto and what I mean by faceting turns into short WOT upright sprints. Do note though a really neutral chassis ain't got to wait for no stinking apex to nail throttle leaned over so 'an' apex don't really apply no more as can make as many as it takes to straighten out the crooks. Personally I think there's a best compromise, too small vs too big per event and bike rider, so nothing for it but spend and spend and spend trail and error till a sense of what suits ya builds up, if not just going by fashion. I only care to ride one special cycle like that anymore.

a 130 rear may foul chain, if can wedge tire past the rear drum, it'll clear the swingarm.

Intresting 1970 spec. Paul Smart at Thruxton , Kuhn Commando ??



Mick Grant , Mallory , 1972 , J.P.N. , Another Pic I read ' Dunlop 4.00 x 18 TYRE ' on Rear Rim .



This I RECALL stated 4.10 19 & 4.25 18 K81s ( TT100 ) ' 850 ' circa 1978 ?? Ran in I.o.M.
around then , I think 107 mph Lap , and 4th ?? in P.R. ?? Supported by ' Thruxton M/C s ?



Race tyres were said to induce weaves through frame inadequacies pre 70s . So ' KR '
used front only for Prod Race Triumphs . :lol: . I would tend to fit the swing arm pivot with a 10 or 20 Ton Hydraulic press , at say 3 1/2 ?? thou. interfearance . OR MORE . Not so as to blow apart cradle mount though . What would it take .?

This is the 75 F-750 , a stop gap as Cosworth hadnt pulled their finger out . :? :roll: . AMOUNGST OTHER PEOPLE . :x



oopsie . :shock: P.R. Commando on right , L is Mick Grant , Jim Lee Commando . maybe 1970

Golly Gee Matt you post some great photo articles. Last one sucks though. What ya really need is at least two sets of wheels, one for tracks and one for traffic. Can't solve our economic problems by Gov't spending more but ya sure can on motorsports!
BTW, are these upper crust race tire bias or radial?

Getting through them . Now . Drove down the shed to pick up the stuff in the corner as the weather beauro is paranoia induceing sugesting 300 mm ( a Good Old FOOT ) of RAIN .
Low and behold , the Fairies had put This One out on the track through the parafanalia . So was ' The Other ' for the 850 P.R. shown above . :mrgreen:
The olde monocule in microns should get the fact that ' its got a bit of rubber on it there ' regeistered .



Had a pic of a 70 Odd Maserati V8 on a dyno . EXHAUST was White Hot , translucent . Bright orange at some bends and a few darker red bits at a tighter bend and a collector / junction .
Have allways considered the open flowing bends to not impede output as silly little tight ones can .In fact was why I didnt run the early PR headers with the Kink at the head on the norton .
Olde BSA & the daytona Triples noteably had open curved bends . The colour matching the temperature , the Masser was about 1100 deg in the pipes . :shock: ' a little bit of Flow ' . :lol:



Something to be said for keeping the throttle W.F.O.

Great old magazine piece - thanks.

Jack Simmons, at the time in Perris, CA, used to rebuild my Ducati single cranks. When Ducati increased the diameter of the replacement crank pins, I "had" to agree with Jack that we "had" to bore the flywheels to fit the new larger pins. Yep, no choice but to bore them offset. Voila - stroker crank. That meant that we had "no choice but to fix the piston crown and chamber too."

B+Bogus said:

I'm starting to get some stuff together to build a Production Racer with a view to doing BEARS racing, but keeping it roadworthy.

I'm debating whether to build the wheels with 18" rims and would welcome comments from folks who know the pros and cons - 'cos I don't!
I see that some 'decent' 19" tyres are becoming available, so perhaps the main argument for changing isn't as strong as it once was?

All comments gratefully received.

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Think this lot lost the plot a bit....so....and I did notice your location is North West UK, for those who don't know the UK BHR is running BEARS for the first time this year.

Last time I rode a Production Racer styled Commando at Cadwell Park was in late 2010, it was fitted with Avon AM22 110/80/18 front and rear, front fitment and rear fitment are different, the front of course is softer compound...too soft for the rear though some turn a front around and use it as a rear in the wet....they work and you will find other BHR BEARS racers will have them fitted. I reckon they will cope with a little road use, they warm fairly quick, but don't expect to go touring.

I shall be using the same tyres at Pembrey with the CRMC at Easter on a Rickman Norton....maybe actually literally since the front end was taken of the PR bike! and I think teh rear tyre was moved as well. But I do have a fresher pair to use if I can get them fitted....may keep them for Cadwell in May since I have only entered 2 races with this bike to see if I can do more than 1/2 a lap like I did last year with it, now it has been reworked.

These are not my bikes by the way, the owner is on here and has been real generous to me over the last couple of years, even if I shall be riding an'85 Gixer as well... :roll: ....at least early season....the Gixer BTW has the same 110/80/18 front, they get a lot of use, including on 350TZs...

Rims WM3/WM4, as kenny says...and Kenny Cummings advice is generally good, but in the UK rely on more wet and cold races than he has to deal with, the Avons are preferred to the Dunlops by many, some who do use Dunlops still swap the Dunlop rear for an AM22 in the wet. This includes Graham Williams who won many races and a championship with the CRMC last year using 750 Seeley and featherbed framed Weslakes...and the championship winner on the 350TZs...who uses the AM22 front wrecks a Dunlop rear in one practice and one race....

Avon lowered their prices for 2012!, not much, but it all helps...I would suggest you give Tony Salt at TST a ring, he has the best UK prices and good delivery.

You will find the AM18 rear 120 being used on at least one BMW in BEARS, but not many use it, in fact I think Avon withdrew it for a while and apparently it works with a heavy bike, so it must be an option, but you will most likely turn alittle quicker on the 110, and if you think about it 110 front and rear is about as close as you will get width wise in a race tyre to that old Commando proddy race favourite the front and rear 4.10 TT100....

If you want a 130 AM23, then if your swinging arm takes it, you will end up trimming the left edge to avoid the chain run....until you have started winning I really would stick with the basics, and be prepared for some very rapid bikes and riders on Italian exotica in BEARS, hope to get to one round at least to watch, we will see.

madass140 said:

big and fat is not necessarily better , leaning over with a big fat rear tire dramatically changes the "wheel alignment" for want of a better term, I realized this when first riding some of the big bikes running 190 rear tires, you really have to hang off the bike to get round a corner, in my early Commando days the best tire combo was a 3:60 x 19 K81 on the front and a 4:10 x 19 K81 on the rear. People raced on these and probably still do.

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Yep, I raced on those TT100s 3.60 front and 4.10 rear on a Proddy Commando in the '70s, but most used the 4.10 front and rear, and some turned the tyres on the rims to get more use on clockwise circuits!

Big is definately not best here....

I just purchased a pair of 4:10K81's made in Asia now and they seem to be a bit softer than the English ones I used to buy many moons ago. For road use I think they will be just perfect.

madass140 said:

I just purchased a pair of 4:10K81's made in Asia now and they seem to be a bit softer than the English ones I used to buy many moons ago. For road use I think they will be just perfect.

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They always used to be the best road tyre on a Commando, so why not...especially if they have improved the compund a little...and 19" is fine too...

The change to 18" has only ever been about the race rubber you can get, I can't see it ever made sense for the road, if you could get what you want in 19" stick with it.....several Commando racers changed to an 18" rear in the '70s to use the KR91, and endurance tyre, but actually the overall rolling diameter was the same as a 19" tyre.

If that confuses B+Bogus, the 19" AM26s have been around a couple of years now are getting a lot of use on featherbed singles and smaller bikes, I think Avon may need to offer a couple of slightly larger sizes to make them more feasible for 750s upward.

And OBTW, I have ridden my '96 Gixer with the standard 190s, no real issue on the road, but on a race track you do need to hang right off, it turns slightly better if you use the 55 profile 190s and not the 50 profiles ones....but then again the steering geometry is so different to a Commando that they are never really stable anyway...so brake late and push hard is the norm, which is why running a very big tyre on a Commando would not make all that much sense even if you could fit it...the geometry is not designed to make use of it...best approach is don't go too deep and make a smoother turn in....classic style....

SteveA said:

....Rims WM3/WM4, as kenny says...and Kenny Cummings advice is generally good, but in the UK rely on more wet and cold races than he has to deal with, the Avons are preferred to the Dunlops by many, some who do use Dunlops still swap the Dunlop rear for an AM22 in the wet. This includes Graham Williams who won many races and a championship with the CRMC last year using 750 Seeley and featherbed framed Weslakes...and the championship winner on the 350TZs...who uses the AM22 front wrecks a Dunlop rear in one practice and one race....

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Thanks Steve. And back at ya; your advice is good. I haven't run on Avons in several years, but from recollection they were excellent in the wet and cold (and Dunlops are definitely not). Having said this (I don't want to say too much negative here, because I have spoken to Dunlop directly on this and they are trying to correct) the last batch of KR164 tires we received here in the US were awful. Tearing and shredding after one good practice. This was acknowledged by Dunlop, as apparently they had to change their process mid-production due to environmental standards. Ooops.

For a racer to change tire brands can be like changing religions (or Irish vs. Scotch whiskey). But believe me, I have considered alternatives lately. Having said this, Dunlop is now supplying a KR145 for the rear this year, and I'm going to give it a go. Do you know anything about this tire?

And finally, I always felt Avon's quality control was better than Dunlop. But for me, what Dunlop had was predictability when you started to slide. By the time I got into a slide on the Avons it was too late.

Hehe, ya only have to be athletic and smooth careful in turns on corner cripples. The worse traction handling and slowest way to take turns is braking while leaned, pashaw. Anything that removes thrust load on rear toward front is not the funnest securest way around to me. Ya can't trust your tire or bike set up until you worked up temps then worked on lean foul limits then worked up throttle till tire lets go, enough times to know exactly what's going to happen ahead of time, then may find worse condition to hold bike in is a constant lean sweeper. Ongoing harsh Gravel travel lesions taught me to only brake full upright before any lean, till *slow* enough I can toss bike over as far as I can under hi power to flash past everyone still hard-ly on brake d/t leaning - so they appear like doddling parking lot cones to swerve around so easy, The fatter the rear the easier they are to ignore as competition in turns. If i see a fork damper i don't even bother sniffing their rear chicken stripe any more.

If ya bike can't handle it like I describe then rest assured you are on a corner cripple and damn better face it and behave accordingly, smooth and slow and steady as she goes, hehehe. I'm a mis fit d/t 3 iso linkages so am the most jerky pilot on forks and throttle and not a model to try to follow. The looser the conditions the more you better only put down very smooth easy forces *or* go a bit berserk with ballistics and break er loose on purpose ahead of time, in best traction, so can be easing up loads at worse traction point where everyone else is tip toeing around so slow and smoothly.

Holmeslice said:

For a racer to change tire brands can be like changing religions (or Irish vs. Scotch whiskey). But believe me, I have considered alternatives lately. Having said this, Dunlop is now supplying a KR145 for the rear this year, and I'm going to give it a go. Do you know anything about this tire?

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I am an Islay Single Malt guy myself, so even harder to please soemtimes, there was a time when I bought nothing but Dunlop for bikes, but running more modern track bikes introduced me to Pirelli superstock tyres and inters....great in damp condidtions but too easy too shred....and now I have found Avon is the most popular in the UK in a lot of applications...and I am not going quick enough I reckon to get too many slides....

Even my '85 Gixer with its short swinging arm was much more stable than I expected at a very variable condition Snetterton last October, front 110/80 was planted and the rear 150/70 was very predictable...started passing people that I wasn't in drier condidtions....but then I had more horsepower to use on the straights which Snetterton has a lot of...

I don't know the 145, I will look over the next few events and try and work out if the Dunlops might be a good direction if I get quicker on the twin, but I reckon the Avons will go a long way before I need better...I am just an old guy playing after all....I rode the Vendetta Mk4 on Dunlops in 2010 and the only comment I had was that the front was over tyred and it would have steered quicker with something a bit smaller, but neither me or the owner are lightweights and the bigger tyre is probably working better on the brakes!

There was a hushed scandal two years ago at Daytona involving the AMA spec tires for the 600s, lots of crashes, guys losing the front end. Before I heard of it, I bought a set of those tires from the West coast distributor for my CBR1000RR and when I had the front end step out unpredictably for the second time, I took them off and threw them away.

Just goes to show ya how stupidly dangerous it is to depend on front tire for about anything but straight line upright braking, unless wisely going so slow it holds front off ground. If ya can't put all attention on the rear patch only, keep working on tires and bike combo's till ya see what's ya missing out on.

Just got back on Trixie, lovely lovely ride. No problemo holding fork angle dampened while the front is sliding and slipping just out short of a take down till they finally catch enough to effect aim in desired direction. Highly recommend practice on lo air'd tires and then on some sand or grit covered hard base so track time is pure relief luxury to have at it.

For a racer to change tire brands can be like changing religions (or Irish vs. Scotch whiskey). But believe me, I have considered alternatives lately. Having said this, Dunlop is now supplying a KR145 for the rear this year, and I'm going to give it a go. Do you know anything about this tire?

Yup, the Avons and Dunlops all have their pros and cons. Living at the end of the supply chain as I have, I'd run on whatever I could get that was fresh. FWIW, I always liked the Avon compounds, but I preferred the Dunlop KR124/164 profiles, there seemed to be more tread at high lean angles. Regardless, a good rider can go quick on either brand tire...

For Northern750, I race with Avons and run the 130/650 rear. I have the swingarm notched out on both sides to accept the tire on a Commando framed race bike.
The Avons AM22/23 are excellent, very sticky and good in the rain (although I slid out in a light shower at Mid-Ohio last year) but Kenny is right that when they go out, they go out- you don't really slide, you are just on the ground wondering what just happened. To even consider putting 19's on a bike you want to take to the track seems insane to me since you will not be able to take advantage of the many excellent rear tires available, all of which are 18's.

madass140 said:

I just purchased a pair of 4:10K81's made in Asia now and they seem to be a bit softer than the English ones I used to buy many moons ago. For road use I think they will be just perfect.

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Yep - I've got a pair on my MkIIa and they're very confidence inspiring, the compound is way softer than the originals (from memory), and the 4.10 on the front doesn't slow the steering down noticeably... but then again I'm used to Ducati's legendary 'tramline' (in other words 'supertanker') handling
No intention of using anything else on the road.

Doug MacRae said:

For Northern750, I race with Avons and run the 130/650 rear. I have the swingarm notched out on both sides to accept the tire on a Commando framed race bike.
The Avons AM22/23 are excellent, very sticky and good in the rain (although I slid out in a light shower at Mid-Ohio last year) but Kenny is right that when they go out, they go out- you don't really slide, you are just on the ground wondering what just happened. To even consider putting 19's on a bike you want to take to the track seems insane to me since you will not be able to take advantage of the many excellent rear tires available, all of which are 18's.

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This is just what I needed - I'll make sure I've got the wheel sorted before I get the swinging arm painted. All the UK-based guys vote the Avons the best, and they're what I run on the road on my T140 and the Duke - now that would be a great BEARS bike, but just too costly if (when) it goes pear-shaped.

As SteveA has pointed out, 19s aren't quite the problem they used to be, and if the Domi goes on the track (which it just might...) I know good tyres are available.

Some pretty compelling evidence here...

http://www.youtube.com/watch?v=Bax6oH6B ... ure=fvwrel

I'm about to order a WM3 & 4 in 18"

I really appreciate the great advice, and those '70's photos are just so inspiring
I'd toyed with the idea of running an 'S' ehxaust system until I saw the photo of the Kuhn bike. Now it's a definite!

Incidentally, I know Tony Salt from the SMD years...time to say hello again.

Does anyone ever test tires to point of slipping out on purpose, so not crashing accidentally?

When I get a bike going that can kick up its heels this is what i'm fitting on rear, pirelli diablo corsa 120/70ZR18