Incredibly Basic Tire Question

[Crash106]

Hello Race Fans,

 

So, if we "stear for the rear," because that's where the most rubber is, and if racers often wash out the front tire from over braking at turn entry, why don't we just put on a wider front tire? Harley-Davidson is doing this on some of their Power Cruisers but I think this is mostly a fashion statement. Would a wider front tire really make the bike THAT much harder to turn?

 

Thanks,

Crash106

[faffi]

Hello Race Fans,

 

So, if we "stear for the rear," because that's where the most rubber is, and if racers often wash out the front tire from over braking at turn entry, why don't we just put on a wider front tire? Harley-Davidson is doing this on some of their Power Cruisers but I think this is mostly a fashion statement. Would a wider front tire really make the bike THAT much harder to turn?

 

Thanks,

Crash106

 

In a word, yes. Although the increased steering effort isn't the biggest problem - torque steering (or what they call it) is. The wider a tyre is, the more leverage bumps etc. has on the tyre, which goes to the steering, which affects the whole bike. This is because the patch of contact is further removed from the bike's centre line. So basically it will be more difficult to control the bike whenever the road isn't perfectly smooth (is it ever?) and the tendency to stand up will increase dramatically.

 

Both Honda (with the early CBR900RR) and Suzuki (with a late GSX-R1100) tried to use 130mm wide fronts. It didn't work out very well. A magazine tested the GSX-R with 120 and 130 mm wide fronts and 180, 190 and 200 mm wide rears and found the 120/180 combo to work best but that the 190 rear gave a little better grip at racing speeds that probably would make racers willing to live with the reduced stability and increased steering effort. The 130 wide front only gave a minute improvement in braking, but was markedly worse at everything else.

 

Cruisers can get away with super-wide tyres because they do not lean as far nor are they ridden nearly as hard. However, they are not fitted for performance (unless the load capacity advantage is required) but for styling.

[Fajita Dave]

It might have something to do with how much load is put on the tire to. If you have a wider tire with the same amount of weight and air pressure you can actually get less grip. The wider tire will hold the weight up more so the tire wont be pushed into the ground as much which creates a smaller contact patch. You could lower the tire pressure to fix that but you still need to deal with everything Eirik mentioned.

 

There is always a point of efficiency and I guess the manufactures found it with the 120. Besides on most corners the faster way around is to get off the brakes earlier and on the throttle sooner. So even if the wider front tire did offer more grip for trail braking it wouldn't really pay out in lap times.

[Crash106]

Great answers. Thank you. I knew there had to be some logical reason. Once again, a perfectly good theory shot in the behind by the real world.

[Cobie Fair]

Interesing info, I'm going to ask Will to have a look up here, see if he has anything to add.

 

For sure that 120 front has been around for a very long time, and while the rears hav gotten larger the front not much so.

 

CF

[Balistic]

The only thing I could add is that bikes with similar front and rear tires steer and turn very well. back in the day of 16" tires we used to put 120 fronts and 130 rears on Ninja 250s and they worked much better than the 100/120s they came with.

 

The other example would be the HDs with 16" front wide (150) tires, like a wide glide. I think the rear is slightly bigger but a 15" wheel making it nearly the same size. They handle great! very light steering and neutral in the corner. Yea I know we are talking half the lean angle but it's still true.