Tyre choice for adventure riding? (Mixing road and off-road)

[brp]

Yeah both built for different purposes.

If I was after tractor like torque I'd be running for The Doctor. Before our excursion to the beach today did some forest track - just magic all
that torque from a thumper, whack through the gears quick and let that torque do all the work and not have to rev the shit out of that big piston

[10bikekid]

Yeah both built for different purposes.

If I was after tractor like torque I'd be running for The Doctor. Before our excursion to the beach today did some forest track - just magic all
that torque from a thumper, whack through the gears quick and let that torque do all the work and not have to rev the shit out of that big piston

Agreed

[Waipukbiker]

Torque is the turning effort imparted to the center of the wheel, eg, if you were able to put a bar on to the center of the wheel and turn it, A bar 1ft long with 1 lb of weight on the end will impart 1 lb ft of torque to the wheel. or, A bar 20 ft long with 1 lb on the end is 20 ft lbs of torque.
Now its all in newton meters so ill try and do an exercise on a my DR650.

Max torque is 54 nm at 4,600 rpm (Apparently) so lets say Im in 3rd gear at 4,600 rpm (Trying to keep up with DR Girl) 3rd gear is 1.238 to 1 so that multiplies the engine torque to 66.85 nm at the C/S Sprocket. Mine has a 15/43 sprocket combo which is 2.86 to 1 so
the theoretical torque available at my back wheel is 191.19 nm. This is never an exact calculation because of what is known as parasitic losses.
In all parts of a drive train there is drag or resistance eg, bearings, seals, oil drag, chains etc, ( also includes any electrical load on the alternator).
Whats left over gets to turn the back wheel.

There is a saying, Horsepower determines top speed , Torque determines how quick you get to that speed.

Hope this makes some sence

[warewolf]

Its like a set of old fashion balancing scales - increase the HP decrease the Torque - well thats what a mate told me - knows a thing or two though

Not quite. HP is simply torque times revs. If you can only make torque at low revs, you don't get any power because there's no high-rev torque, a la H-D. If you only make a little bit of torque, but can rev to the moon, then you get decent top-end power but no bottom-end, a la 250cc IL4. Both of those types of bikes are the extreme ends of the range, there is a heap of middle ground. Generally speaking, anything that improves the engine's efficiency makes both more torque and more power; modest gains in each makes for an overall improvement. But if you want big HP numbers then some of the things that generate high-rev torque aren't compatible with low-rev torque, so you must choose. (And I would add, for both the aforementioned styles, what you have been told is more the truth, probably because they aren't efficient designs to start with, or they are already extremely biased in their tuning.)

My Triumph Trophy was re-worked for more midrange - and I would not do any modification that sacrificed it for top end. The bike ended up with 50% more power than stock, with more power & torque everywhere in the rev range vs a stocker. So you can have your cake and eat it, too, if you go about it the right way. I could have got more HP but wasn't interested in a big top-end number, rather get-up-and-go in the middle. 10% more was cheap, but the rest was not!!

[dino3310]

Ran 25psi rear and 28 front today colin.... felt much better.
cheers for all the tyre advice/knowledge

[brp]

(And I would add, for both the aforementioned styles, what you have been told is more the truth, probably because they aren't efficient designs to start with, or they are already extremely biased in their tuning.)

Yeah that's what he was getting at, cheers.

Is it the laws pf physics coming into play ? - Motors that produce large torque usually have large pistons with a large stroke - and can't rev out the same (with most V8's redlining 6500 RPM if you are lucky - if its a mighty Ford V8 add bit more )

XR has a set up to stop windage loss from the alternator, interesting to see it all counts where it should.

Did ya do ya valves etc on ya trophy - how did ya have ya cake and pig out on it to ?
How could low down torque be increased on the XR ?


Thanks for Waipukbiker for the torque explanation

[Night Falcon]

Torque is the turning effort imparted to the center of the wheel, eg, if you were able to put a bar on to the center of the wheel and turn it, A bar 1ft long with 1 lb of weight on the end will impart 1 lb ft of torque to the wheel. or, A bar 20 ft long with 1 lb on the end is 20 ft lbs of torque.
Now its all in newton meters so ill try and do an exercise on a my DR650.

Max torque is 54 nm at 4,600 rpm (Apparently) so lets say Im in 3rd gear at 4,600 rpm (Trying to keep up with DR Girl) 3rd gear is 1.238 to 1 so that multiplies the engine torque to 66.85 nm at the C/S Sprocket. Mine has a 15/43 sprocket combo which is 2.86 to 1 so
the theoretical torque available at my back wheel is 191.19 nm. This is never an exact calculation because of what is known as parasitic losses.
In all parts of a drive train there is drag or resistance eg, bearings, seals, oil drag, chains etc, ( also includes any electrical load on the alternator).
Whats left over gets to turn the back wheel.

There is a saying, Horsepower determines top speed , Torque determines how quick you get to that speed.

Hope this makes some sence

I understood everything up to "Torque is"

[Waipukbiker]

If I reprint it in orange text, would that help? or try a couple of these first Hope you have a good ride in the weekend.

[Night Falcon]

If I reprint it in orange text, would that help? or try a couple of these first Hope you have a good ride in the weekend.

no I'm just as thick in orange. Went for a test spin up the gwavas yesterday, great fun poking the 690 into places it shouldn't go. But I have to say I'm well impressed with the MT21 front. Stearing is far more positive on gravel and holds real well in sand & clay. I didn't realise what I was missing!

[JATZ]

My Triumph Trophy was re-worked for more midrange - and I would not do any modification that sacrificed it for top end. The bike ended up with 50% more power than stock, with more power & torque everywhere in the rev range vs a stocker !

Did ya do ya valves etc on ya trophy - how did ya have ya cake and pig out on it to ?

And a very nice cake it was too Werewolf can probably fill in the details on what was done internaly but I know it went kinda quick even 2 up with a bit of gear. Not only was the power upgraded but equally importantly the suspension was too. The brakes were not to shabby either.
Back on topic, this is a tyre thread after all.....it had tyres both on the front and on the back, weird aye
Here it is from a weekend trip to Bluff via Tekapo, see the tyres

[Waipukbiker]

Sounds good about the MT21, happy with it on the seal?
Its when the seal is wet that I get a bit nervous but just means riding to the conditions.

[Night Falcon]

Sounds good about the MT21, happy with it on the seal?
Its when the seal is wet that I get a bit nervous but just means riding to the conditions.

so far its been great on the seal. Gave it a good flogging yesterday and it held up just fine!

[Woodman]

MT21 front is a great tyre, well priced too. My front tyre of choice now, only issue I have is that they have a tendency to lock up under hard braking, even with the KLR crappy front brake.

Rears are good too, but some guys hate them on the rear.

[warewolf]

Is it the laws pf physics coming into play ? - Motors that produce large torque usually have large pistons with a large stroke - and can't rev out the same

Yep, it's all physics. One of the big issues is that things are different at low vs high rpm. Some examples:

• Gas flow speed needs to be high for best efficiency. You want high gas speed intake to atomise the fuel droplets coming out of the carb jets, and high gas speed in the exhaust to help draw the spent gases out and fresh charge in. A narrow pipe gives high gas speed at low engine speed (low gas volume) but this will limit gas volume at high engine speed. A wide pipe that flows massive amounts at high rpm will have a very low gas speed at low engine speed, so low end efficiency suffers.
• Valve duration is set as a number of degrees on the camshaft. It needs to be long at high rpm because the "per minute" thing comes in to play and you need time to get the gases in to the cylinder. But at low rpm the valves are open for too long for best efficiency. You've probably heard the expression "lumpy cam" and heard race engines that just don't sound like they are running right at idle. In a similar way, two strokes have port timing, and when the revs come up to where the timing is optimised, sh!t happens as it "hits (power-)band" or comes "on the pipe" (which is why 2Ts have lots of ways of varying the exhaust timing).
• Yes, piston & valve mass is a rev-limiting factor. The big pistons in a 1340 cc H-D twin are stressed far more at 5000 rpm than the tiddlers in a 250cc IL4 at 20,000 rpm, due the square- and cube-law multipliers of mass vs force vs velocity. You don't need a large piston or long stroke for torque, there are other design factors.

It's a big topic, but there are plenty of good books on the subject. Nelson folks are welcome to borrow some of mine if they are interested.

Did ya do ya valves etc on ya trophy - how did ya have ya cake and pig out on it to ?

Yes. The cheap mods: plane the head to increase compression (positive side effect of increasing the ignition advance), quick port job to remove the worst of the manufacturing goofs and very minor improvement on only one side that suffered (in or ex, can't remember), after-market touring mufflers (not loud), dynojet kit to suit, K&N air filter, removed the manufacturing goofs in the header collets and the balance pipe. With those mods, it would pull 6th in the midrange (overtaking) like it used to pull 4th. I kept finding myself a gear or two higher than expected. Also at that time, fitted Ohlins fork springs and a Daytona-spec Ohlins shock. No good having all that power if you can't get it to the ground; the std suspension did the whole "squat and push" thing exiting a corner whereas the Ohlins let you wind on the throttle and just DRIVE outta there! Braided steel brake lines rounded out the package.

The expensive mods: high-compression Daytona Super III pistons (12:1 vs 10.3:1) which along with the planed head took compression to 13.9:1, Daytona Super III camshafts (wildest cams Triumph did, huge lift and long duration), improved cut on the valve seats to match the back-cut valves (material removed from the stem side to improve flow at initial valve lift), about 50 hours of porting work on the head (not charged because the technician was a fellow enthusiast and had time to spare in winter), removed some flow-restricting pre-filters in the airbox, and dyno tuned to suit. We tried to use the stock air filter since the K&N flows more dirt and the bike did lots of gravel roads, but she was a long way past the flow capabilities of the stock one! And the only reason it could run pump gas at 13.9:1 CR was that the cams were such long duration that the dynamic CR was much less: the piston was a long way up from BDC before the valves closed. Since I couldn't get the front end working right, in went RaceTech Gold Valve Emulators, and Robert Taylor retuned the rear shock and increased the ride height to stand the bike on it's nose to quicken the steering. I also dropped the gearing 7% which made it a bit short, but helped getting going two-up with gear especially uphill. I was going to go +3% on the next sprocket change to work the midrange more.

Don't forget that the 1st generation Hinckley Triumphs were quite conservative: low redline and low power compared to similar Jap machinery. One thing I didn't do with mine was chase up a 750cc igniter box that would increase redline from 9500 to 11000rpm. The thing hit the rev limiter while the power was still climbing sharply, so there was more there if I could let it rev out.

Conflicting things - or compromises: the std headers & touring mufflers while much improved did not flow high-rev like a race exhaust, but helped the bottom/mid. The super-high compression created a thin combustion chamber; I often wondered if a second head gasket would drop the CR and improve high-rev combustion, at the expense of the low-end. Drag racers love compression to get them off the line. The wild cams certainly gave the bottom-end grief, but everything was so much improved that it was still better than std. The valve work improved everything, as did the porting.

These sort of gains are likely achievable on "trail" bikes like the XT, DR, KLR, XL with modest power outputs. Enduro bikes like the XR, TT, KLX, EXC will already have pushed the design further so gains will be harder to come by.

Tyre content: the better I got the suspension working, the less chewed-out the tyres got, and the longer they lasted, despite the power & torque increase.

How could low down torque be increased on the XR ?

Plane the head. Refresh the valves: make sure the seat faces are in good shape. If running the OEM exhaust, clean up the collets and anywhere else the manufacturing is less than ideal. Mild port work. A loud high-flow exhaust probably won't help if the rest of the system is still constricted. Research what other owners do, and what performance shops do.

I should add that cubes is an easy way to power & torque, as is gearing. And a more modern bike will usually be a much better overall package: trading up may be more cost-effective.

[brp]

Cheers for the pic JATZ - that breed of dog deserves a pedestal - not that I'm Bias Good skills getting the beaut trumpet into position

Wow Colin you know your stuff - no wonder your mods to the green beast made it haul

Enduro bikes like the XR, TT, KLX, EXC will already have pushed the design further so gains will be harder to come by.

Too true, I can see Honda has already included many of your points for low to mid range. Could always go for the 65 HP HRC kit or go further with the 680 cc kit or the whole hog with the 700 cc kit. More curiosity the question on increasing low down torque, happy with the status quo - tyres will thank me for it too