Longer Rear Shocks

Dances with Shrapnel said:

there are clear benefits to quicker steering turn in as a result of raising the rear 10-20mm.

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I agree. I had a Ducati ST4s that had a great four vv 996 motor, and Ohlins. But it was a bit heavy and slow handling. I raised the ride height 20-mm in the rear and it made it so much quicker handling. No real downside to stability at speed that I could see, and had it on the track a few times.

gortnipper said:

I agree. I had a Ducati ST4s that had a great four vv 996 motor, and Ohlins. But it was a bit heavy and slow handling. I raised the ride height 20-mm in the rear and it made it so much quicker handling. No real downside to stability at speed that I could see, and had it on the track a few times.

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Well, general consensus here seems raising the rear results in quicker handling without downsides. So why didn't motorcycle factories design it right in the first place?? Like Dances with Scrapnel mentioned "It's not so black and white" there is a lot more to it. The racing motorcycle by John Bradley is for instance a very explanatory book on this subject.

nortonspeed said:

Well, general consensus here seems raising the rear results in quicker handling without downsides. So why didn't motorcycle factories design it right in the first place?? Like Dances with Scrapnel mentioned "It's not so black and white" there is a lot more to it. The racing motorcycle by John Bradley is for instance a very explanatory book on this subject.

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Ok. On my reading list now.

Have a good friend who owns a dealership. He says the lower a bike is the easier it is to sell.
In so many ways, bikes are configured just to get them off the sales floor.

Dutch said:

Have a good friend who owns a dealership. He says the lower a bike is the easier it is to sell.
In so many ways, bikes are configured just to get them off the sales floor.

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Probably an awful lot of truth there, with regards to many aspects!

nortonspeed said:

Well, general consensus here seems raising the rear results in quicker handling without downsides. So why didn't motorcycle factories design it right in the first place?? Like Dances with Scrapnel mentioned "It's not so black and white" there is a lot more to it. The racing motorcycle by John Bradley is for instance a very explanatory book on this subject.

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In Australia, a lot of guys do historic racing with old converted road bikes. Most road bikes are constructed so they do not neck the riders. So a converted road bike is never as good as a genuine race bike. Quick steering is good on a race bike, but can be dangerous on a road bike. The first Commandos had steering geometry which was specified by Peter Williams and a few inexperienced riders crashed in the wet after riding over cats' eyes. The next models had slower steering. The first model Commando would probably be a better race bike than the later one. If you think about it, the change in rake as you brake and accelerate must be fractions of a degree, so messing with the frame geometry can be very dangerous. When I do mods, I always ride the bike first time, somewhere where I can crash safely and I take careful note about how the bike is responding before I get silly.
If your bike is too stable, it can tend to rise as you brake into corners, - if your steering is really quick, if you gas the bike hard when halfway around a corner, it can self-steer itself the rest of the way around the corner.
My bike steers too quickly for anyone but an idiot. You put your mind where you want it to be and it is there.

I should add, relative to the question asked, my shocks are 13” eye to eye but I have also raised the front end with the Fauth kit. So, the whole bike is raised such that I have to be going pretty fast and catch a bump before my head pipes scrape

nortonspeed said:

So why didn't motorcycle factories design it right in the first place??

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Of course the most obvious answer is: "because that's the way we have always done it!"

The challenge is determining "what is right" in the first place. What is right for the masses is not necessarily what is right for a club level racer or a more skilled and knowledgeable rider.

One could conduct a parametric analysis of historical data and maybe supplement it by taking a pole here to determine how many have changed the rake angle (+ or -) on their Commando and by how many degrees. If you throw out the chopper crowd, I venture to say the vast majority of the distribution will be towards decreasing rake angle - just a hunch.

If we keep this in the context of the original posters questions and assertions, yes, raising the rear through longer shocks several mm will quicken the steering and no it will not create an untenable situation. With Commando based racers it is a common practice to do exactly that.

xbacksideslider said:

I should add, relative to the question asked, my shocks are 13” eye to eye but I have also raised the front end with the Fauth kit. So, the whole bike is raised such that I have to be going pretty fast and catch a bump before my head pipes scrape

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Longer shocks with softer springs might bring the rear down to the previous level and give more squat under acceleration, so the ride height at the front would not need to be altered. In the end, you usually have preload adjustment on the rear shocks which can make the system sensible. The main thing is to avoid any really bad effects, so make progress slowly and be aware of how your bike is handling. If something bad is going to happen, there are usually warning signs. If you end up with more travel and more rear end squat, your bike will probably be more responsive in corners.
Tony Foale had a bike set up on which the rake could be altered. He said the limit effects are extremely stable and self-steering. However handling od a combination of rake and trail. 1962 model Manx Nortons have 24.5 degree rake and very short yoke offset (so relatively a lot of trail ?) - they tighten their line considerably when gassed hard coming out of corners, cranked over.

I once greatly improved the handling of a T250 Suzuki, by laying the shocks down and pushing the rear end up. When I sat on the bike, it came back to level, but the change in spring rate gave the rear end more squat under acceleration. A T250 usually has very neutral handling, but that one was ace in corners.

You have a problem with a standard Commando. You cannot push the fork yokes up and down the stanchions to get rake and trail adjustment. So what you do with the rear shocks is more important.

acotrel said:

You have a problem with a standard Commando. You cannot push the fork yokes up and down the stanchions to get rake and trail adjustment. So what you do with the rear shocks is more important.

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There is a solution to that problem, here is what I did on my Commando: replaced the front Commando stanchions for Dominator stanchions (32mm lower), changed stock shocks with 313mm IKON's. So on balance I raised the rear with 14mm plus lowered the centre of gravity resulting in quicker steering. Also tugged in the exhaust pipes as much as possible (in combination with rear sets) and replaced the stock centre stand for a custom made smaller one to keep enough ground clearance.

The problem with any of this stuff is that the mods are usually expensive and a lot of it is 'suck it and see'. In my own case, I came to a good answer by sheer arse - although I had a slight idea what to expect. When I was a kid, I crashed at Phillip Island about four time in one day, due to a dragging front brake which ran me off into the bush a few times before locking and launching me. I never knew how stable a bike becomes when the front brake stays on.

nortonspeed said:

There is a solution to that problem, here is what I did on my Commando: replaced the front Commando stanchions for Dominator stanchions (32mm lower), changed stock shocks with 313mm IKON's. So on balance I raised the rear with 14mm plus lowered the centre of gravity resulting in quicker steering. Also tugged in the exhaust pipes as much as possible (in combination with rear sets) and replaced the stock centre stand for a custom made smaller one to keep enough ground clearance.

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Well, that’s very different to simply ‘fitting shorter shocks’ now isn’t it?!

Fast Eddie said:

Well, that’s very different to simply ‘fitting shorter shocks’ now isn’t it?!

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Yes Sir, I stand corrected

Well, it is “stand to be corrected”. Visualize that British student in knickers and vest having incorrectly recited something in class and now having to stand to be corrected. You know we are very formal here.

My friend is British. I once mentioned to him about the Brits' use of the English language to have a go at each other. He said ' they make it an art form'. I got the feeling when I was in the UK, that their education system must be superior to the one we have in Australia. The level of conversation in their pubs is better.

Or, it is a form of the past tense.

'Stand corrected' might be slang, but it really means something to me. - I have a stepdaughter who brings her 3 kids to live with me every second week, as part of a custody arrangement. A lot of her behaviour is outrageous. My main complaint about her is that she will never stand corrected, when she gets pulled into gear for it. She is always on for a fight.

acotrel said:

...................The level of conversation in their pubs is better.

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It may have been once!