Thunderhill Raceway Park, CA
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Bike: 09 Yamaha R1
Forks: 08 R1 with Ohlns 25mm fork cartridges
Shock: Yacugar race shock
Fork height at +4mm
Fork preload 6 turns in (1.0kg springs)
Fork rebound 14 clicks out
Fork compression 5 clicks out
Shock at 295mm
Preload at 4.5 lines (11kg spring)
High speed compression at 21 clicks out
Low speed compression at 18 clicks out
Rebound at 32 clicks out
Gearing: one tooth down on the countershaft sprocket, stock chain
- scrub in tires (cold, no tire warmers)
- 30psi cold rear, 32psi cold front
- assess geometry and chassis
- tires felt ready to go after half a lap
- front gain of 6psi rear gain of 5psi hot off the track
- excellent stability under braking with little sidewall deflection
- excellent drive grip off fast corners
- bike would initiate turns and flick extremely easily
- too much weight bias forward effecting braking performance
Given the braking stability and acceleration grip the cold pressure was a good starting point. The front tire was obviously smaller as I could get my hand under the front fender so the geometry problem was not a surprise with aggressive braking. Having to manage braking is not an ideal situation at all and that by default means a lot less travel available. Normally the zip tie is 3mm from the axle casting.
As an experiment, remove 1.5 turns of rear ride height from the shock to “flatten” the chassis a little and assess the effect on geometry and braking.
- brake hard in turns 9 and 14 to assess weight transfer
- assess change on chassis geometry for flickability
- uphill braking in Turn 9 excellent
- downhill braking in Turn 14 improved
- bike not as flickable, much more work to turn the bike
The rear ride height change validated the need to raise the front end while also validating the need to raise the entire bike back up to get the flickability back.. Fork height was changed to +2mm and the shock ride height of 1.5 turns was put back in.
- assess turn in on high speed turns 1 and 8
- assess flickability in turns 4 and 11/12
- assess braking in Turn 14
- much more precise turn in at high speed corners with gentle pressure needed
- chassis flicked left to right with a little input (that’s what I want)
- downhill braking was as hard as I liked rather than manage braking
- excellent trail braking grip on the front tire
At this point the basic layout of the chassis was completed. I would consider raising the forks 1mm and adding 1mm of rear ride height as an experiment to see how that effected the chassis on high speed turns and quick change of direction corners.
- tires warm up quickly making the rider feel as though they are ready after less than one lap
- great braking stability in the front tire in hard braking
- front tire carcass gives excellent feel while trail braking
- good acceleration grip off the fast corners with little sidewall deflection, but yet to test edge grip based on swing arm angle
- hot pressures may need to be decreased as there were very few and small sized balls of rubber on the edges of the front and rear tire.
Tire wear pictures:
This is the fast side of the tire that experiences the heaviest trail braking and the balls of rubber on the edge of the tread are almost non-existent. That’s unusual by Bridgestone tire wear standards hence the comment on reducing hot pressure to see what happens to grip levels under severe trail braking.
This is the fast side of the tire and the balls of rubber on the edge of the tread are very small by Bridgestone standards hence the comment on reducing hot pressure to see what happens to grip levels.
Image Courtesy of Dito Milian of Gotbluemilk Photography.
Bridgestone S20 tire test Part 2
6/28 & 29: Thunderhill Raceway Park, Willows CA
Ambient temps in the 90’s with track temps at 118F
For the second part of the test, I wanted to run the tires after the initial test of 4 sessions with scrub in and suspension/geometry changes to get the chassis set up correctly. For the morning I left the pressure set at 30 rear and 32 front set as cold at 7.00am with ambient temps in the high 50’s.
The goal was to put the tires under some serious duress with a decent A track day pace close to 2 minutes on this 3 mile flowing and rhythmical course. In the first session the tires were scrubbed in and the course evaluated (half the track was covered in oil from a classic car race the weekend prior from T1 to T6). The course was very slippery in the morning so the pace was delayed until the afternoon when the track had been saturated with bikes for 3 hours to get rid of the dust etc and lay some fresh rubber down.
By 2pm the track was ready to go and there was plenty of open track in the last hour. At this point in the day I was approaching 300 miles on the tires at the same track so it was going to be an interesting test given the track conditions. I went in 6 lap bursts to simulate a race pace using 1000cc bike lines with lots of trail braking and heavy acceleration out of the corners.
Trail braking gave consistent grip, with good feel. I didn’t have to go beyond normal aggressive trail braking to make a pass so I cannot comment on the tires ability to cope with that level of duress. Very consistent feel on the sidewall and upper area especially at the release phase of trail braking.
Acceleration was excellent – solid drive grip with no spin at all. That may be due to the point and shoot style of riding a 1000 so throttle on the edge of the tire with 600’s or smaller bikes needs to be tested.
After a very fast in lap, hot pressures were reduced for the next test.
I decided to drop the hot tire pressure by 2psi to see if I could get a little better feel for the track in general especially during turn in. The tires turned in just the same and certainly gave a lot more information to me but after 4 laps started to feel greasy and that was verified on the last lap with a profound front slide in T2 and a rear tire slide in T6. So at last we had managed to make the tire lose grip. Higher cold pressures therefore are mandatory in warmer climates!
The rear tire while showing excellent wear also started to show the left side becoming shaved/flat spotted in the acceleration area. It did effect turn in nor did I feel the rear flop onto that area of the tire (it doesn’t show clearly in the pictures of the rear tire).
- I am still amazed that after 1/2 a lap the tire feels like it is ready to go. Don’t do that of course and finish a couple of laps or 10-15 miles on the street before you get enthusiastic.
- the tires give prolonged feel and grip that doesn’t change
- the tires are pressure sensitive and 30 rear 32 front would be a good minimum starting point. As always, find pressures that work for you, your bike, track or road and your riding style.
- tire feel with the soft carcass but firm sidewall gives lots of feedback to let you know what is going on underneath you
- I’d choose these over the BT 003RS and the venerable BT 016 in a heart beat!
What a great tire and to be honest a complete surprise to me. Once the chassis and suspension were set, the S20′s made me want to ride.
Front tire, end of test:
Rear tire end of 2 days:
On track narrated video’s from the tire test are here:
Part 1: http://youtu.be/D5bA19e98u4
Part 2: http://youtu.be/2EhMX14Q6X4