7 replies to this topic

[Jez]

Hi all,

In the quest for a sticky front tyre and quicker steering I have an exup front wheel, which will be going on once it is painted, which is significantly wider than stock.

Does anyone know how stability will be affected when fitting a wide front tyre. Drag bikes use a skinny front so will a wide one upset or improve straight line stability? Will it notice? Is there any mileage in fitting a wider rear to compensate?

BTW I have started a new thread about choice of rear wheel here

[robelst]

Wider tyres have a bigger footprint, unless the rim they are fitted on isn't wide enough (tyre will be pushed into a pear-shape: not uncommon in speed-freak streetfighter land).
A bigger footprint means more grip so higher cornering speeds but also more convincing is needed to get it into that corner, and usually lines on roads are more noticeable while braking in corners can set the bike more upright.
I would have thought though that on good quality tarmac stability will be better rather than less?

A friend of mine has got an old BMW R90S, running very slim BT45 tyres (I think the rear is only 120 ): This bike handles like a pushbike and is extremely neutral (esp if you just come from a modern bike with, say 120 front/180 rear) while the modern compound offers enough grip to get the 65-70 bhp on the road. I admit it handles so wel it can almost feel unsettled but that is probably also because of the modest suspension (1980's-design Koni) and jumpy shaft-drive. On the motorway at 100 mph it's as stable as anything. It makes you wonder what the heck we are doing with GP-sized tyres (or even wider ) on our street-machines, even the ones with modest power But then again, for many bikes are more a fashion statement than a riding apparatus

Edited by robelst, 09 March 2007 - 01:42 pm.

[JBX]

Some time ago I had the front tyre changed - a BT020.
The guy made a mistake - he mistook the 900 for a 850, that's sooooo stupid - and fitted a 110 in place of a regular 120.
I didn't notice it at once, shame on me !
The bike handled ok in straight lines but was very unstable in curves.
I then noticed the problem & went back to the shop quickly...

Another story : I saw once in Corsica a TDM900 with a 180 at the rear and asked the owner about handling.
He said it was ok and had more grip (roads there are very curvy), he also showed me the footpegs as an evidence.

[robelst]

Another story : I saw once in Corsica a TDM900 with a 180 at the rear and asked the owner about handling.
He said it was ok and had more grip (roads there are very curvy), he also showed me the footpegs as an evidence.

If that 180 was fitted on a standard rim (5" wide or maybe even less?) then the tyre would have bulged out, most likely leading to less rather than more grip The steep side-walls would explain the foot-pegs though Most people riding around like that usually claim it's grand but usually the only thing that improves are the looks. If a different size were better, wouldn't the manufacturer fit that as standard?

Edited by robelst, 09 March 2007 - 06:56 pm.

[JBX]

I agree...
I forgot to tell that roads in Corsica have a very high grip (granit based tarmac) and the guy had the rear spring at the lowest rate.
This explains the footpeg story, not the tyre size.

[Drew48]

Hi all,

In the quest for a sticky front tyre and quicker steering I have an exup front wheel, which will be going on once it is painted, which is significantly wider than stock.

Does anyone know how stability will be affected when fitting a wide front tyre. Drag bikes use a skinny front so will a wide one upset or improve straight line stability? Will it notice? Is there any mileage in fitting a wider rear to compensate?

BTW I have started a new thread about choice of rear wheel here

17" on the front ( I used a Tcat wheel running 120/70-17 ) improved things no end in my opinion quickened up the steering didn't seem to have any probs with stability - drag bikes aren't really made for cornering. I could have and was going to try a 110 section on it but then I wrote the bike off & there didn't really seem any point I kept the 150 rear 'cos never gave any probs, just sometimes I found the 18" front abit vague admittedly I was running 020's which have never really got on with

[Jez]

I forgot to tell that roads in Corsica have a very high grip (granit based tarmac)

If you are trying to make us jealous you have succeeded with me

17" on the front ( I used a Tcat wheel running 120/70-17 ) improved things no end in my opinion quickened up the steering didn't seem to have any probs with stability - drag bikes aren't really made for cornering. I could have and was going to try a 110 section on it but then I wrote the bike off & there didn't really seem any point I kept the 150 rear 'cos never gave any probs, just sometimes I found the 18" front abit vague admittedly I was running 020's which have never really got on with

That is exactly my point about cornering. They have skinny fronts and fat backs for stability (among other reasons). Thanks for this info, nhs, it is exactly what I was hoping to hear .