Time on my hands...

[exoticices]

In the unlikely event of me winning the lottery, I would run a HP2 Sport race team in international road racing (TT, etc.). This scenario is rather unlikely though, because I don't buy lottery tickets.

I've always wondered how well the HP2 Sport (or R1200S Rennboxer, as it was known) would fare at the TT. Obviously it wouldn't win, but just how far could we push cutting-edge obsolete air-cooled technology? So, using finger-in-the-air research and back-of-fag-packet mathematics, this is what I came up with.

Looking at the fastest lap times of the 2007 and 2008 endurance championships, the Rennboxer was on average 4.15% slower than the winning bike (usually the SERT Suzuki). If we compare this to the winning TT bikes of the period - the McGuinness and Martin Hondas - their average fastest lap was 17m 29.79 / 129.39 mph. Using our 4.15% ballpark figure, all other things being equal (which they won't be!), the Rennboxer would have a lap time of 18m 13.36 / 124.23 mph, which is pretty decent and would give roughly a top 20 finish. This figure seems about right, as it's similar to Michael Dunlop's then-record Classic TT lap of 18m 01.762 / 125.562 mph on the fast-yet-dinosaur air-cooled XR69 Suzuki.

But it's not quite that straightforward! Works rider Richard Cooper said that the Rennboxer was very economical and they could get 30-45 minutes more track time between pit stops than the works superbikes; this opens up the possibility that the Rennboxer could complete a 6-lap Senior TT with only 1 pit stop (rather than the usual 2)! (This used to be allowed, although I'm not sure if it is nowadays.) A good TT pit stop is just under a minute, so if you took a minute off a Rennboxer's theoretical race time, you could be looking at a top 10 finish!

Maybe I should start buying lottery tickets...

[Paul]

Nice work John. Now if you could just run the numbers for a fat middle-aged bloke on an R1250GS (no panniers, but I'd keep the top box on), so I can determine whether it's worth putting in a speculative entry form for 2022. Not sure what class that would run in tho'? I think we can confidently eliminate "lightweight" from the list of potential candidates.

Cheers,

Paul

[Topcat]

Very interesting post, thanks for that.

So the superbike pit stops are governed by fuel and not rear tyres?

[andy griff]

Great post, I'll put it down as one good thing to come from lockdown.
Fuel would be the issue. Max 24 litre tank allowed so the question is would you do a lap on 8 litres , i.e. 38mpg. Seems a bit optimistic. I do recall a 3 lap lightweight race where various teams were considering a no pit stop strategy but the organisers inserted a mandatory stop.

So, if a one- stop plan would not work then another option is to put less fuel in at every stage . So start with less than 24l so reducing weight and improving handling from the get, less tyre wear and so no need for tyres at the first stop. The add only whatever is needed for 2 stops.
If the bike will do a lap on 9 litres then that's potentially a 6l saving at each stage saving weight and time.

I'll leave you to do the sums but happy to sign for the team as race strategy consultant and reserve rider .

[SP250]

I learnt to gas weld aluminium from exactly this scenario.
1979 Manx GP, 350 TZ Yamaha would only do 2 and a half laps on a tank full to the brim, so I cut the top off, welded a 2" strip of duralumin edge on and re-welded the top back on. The extra gallon and a bit just enabled me to do 3 laps.
So in a 6 lap race, you get 3 flying laps instead of, with two pitstops, you only got 1 flying lap.
Huge difference in overall race time.
Broke the chassis from vibration on the third lap and was kept in the pits at the refuelling stop by the marshalls - so a DNF.
No wheel/tyre changes back in the day with only about 80bhp.

[Topcat]

Didn't someone try changing the tanks instead of filling up at the pit stop?

I seem to remember they filled the tank from underneath - upside down - to get as much in as possible and swapped tanks at the pit stop?

[Blackal]

I'm sure I read somewhere that the HP2s did well at endurance racing due in part to the fuel-range of each tankful.

That might work when it is something like 500miles, where the number of stops mean that ending the race with half a tank - makes little difference, but when you try to work that into a short(ish) race of 4 laps or 6 laps of a long circuit - that the stops can not be planned so optimally.

On a short-circuit endurance race of (I don't know) 300 laps - you come in pretty much exactly in accordance with fuel requirement. 37mile laps don't allow that.

I think the other thing would be that while telelever flatters us amateurs - the 'real' road-racers would find it a hinderance, I think.

I can't remember what the fuel consumption was like on my BCR on track-days, but it was pretty horrendous.

[andy griff]

Didn't someone try changing the tanks instead of filling up at the pit stop?

I seem to remember they filled the tank from underneath - upside down - to get as much in as possible and swapped tanks at the pit stop?

Tanks all run under the seat now so that would not work on today's bikes.