Better steering: 750 vs 850 frames (2014)

Which is better and for what?

20 years ago, some Norton specialist in the UK told me to look for a 850 frame and yokes, due to its better steering angle. That was the frame to build a hot bike on.
I recently heard that is untrue, that the 750 has a better steering angle and will turn quicker in.

Does it really make a difference? I see some of the vintage Norton race bikes seem to have tight angles and 18" wheels but the original production racer was based on a 750 frame and 19", is there any correlation?

The 750 steering geometry allows quicker steering, while the 850 geometry supposedly gives a more solid and stable feel, whether one can be considered better than the other I think is going to be a matter of choice-depending on riding style and use.

I have owned both

the 850 tends to hold a line better with less twitchyness

is it because of increased wheel base or steering head angle?

I have tasted four 750's and two 850 both on and off road so my opinion is the 850 is distinctly more sluggish/effort/discouraging to do stuff like change lanes fast, zig zagging or to move forks fast to compensate for the snatching steering forces on grass or Gravel paths, while the 750's made me want to act like a stunt biker on or off road with distinctly less effort discouraging such bad behavior. On the other hand 850 with their short spurt of extra torque even loaded with camp cargo can be very hard to scary to hang with in Mt curves by a hot 750 or other sharper steering modern sports bikes. I did not find either giving a twitchy unstable security sense to hold a line or turn at high speeds, ie: over 90 where the 850 ran out of pull compared to the 3 Combats and one standard '71.

Can't tell any difference on mine. I do have 750 triple clamps on the 850 though.

1up3down said:

the 850 tends to hold a line better with less twitchyness

is it because of increased wheel base or steering head angle?

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The published wheel base dimension of 56.75 inches never changed. Although the rake angle of the 850 frame increased (by 1.0 degree) to 28 degrees, the 850 ("ANG" marked) yokes set the fork legs at a steeper angle in relation to the steering stem, therefore the forks are not parallel with the steering axis. I believe it's the increase in the amount of "trail" (due to the overall change of geometry) that is responsible for the improved stability of the 850.

Frames are the same.

swooshdave said:

Frames are the same.

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There's 1.0 degree difference in steering angle between the 750 and 850 frames, supposedly? :?

thanks for the correct explanation, LAB

in addition the 850s have a more beefier swing arm, box section for less flex maybe?

my 850 is plenty "flickable", yet holds its line better than my 750s especially so in cross winds and rain grooves

L.A.B. said:

I believe it's the increase in the amount of "trail" (due to the overall change of geometry) that is responsible for the improved stability of the 850.

Click to expand...

To me this begs the question, does adding stability take away feel and responsiveness.

To me this begs the question, does adding stability take away feel and responsiveness.

Click to expand...

well, Norton didn't think so and so they made what they felt were improvements on the 850

probably based upon input from their test riders and reports from dealers and customers

I read somewhere that the first commandos were set up with quick steering and a few guys in the UK got chucked over the handlebars after riding over the 'cat's eyes' in the middle of their roads. This was fixed on the next model, I believe by increasing the trail. If you increase the trail too much the bike becomes more stable, however more likely to stand up and turn the wrong way under brakes, and throw you off-balance. If you decrease the trail too much, the steering becomes vey quick, less stable and the bike tends to oversteer as you accelerate out of corners. I use the latter situation to my advantage on my Seeley 850, however I never ride the bike without an hydraulic steering damper. You can change the trail at any given steering head angle, by altering the fork yokes or wheel size, however be careful with your tyre choice and the rear shock settings. As the bike squats under acceleration, the steering head angle changes - that is why the bike self steers under power. If you play with this take care when riding the bike immediately after making changes, and take care to recognize it's natural handling tendencies.
It pays to use a magnetic base protractor to measure the steering head angle, also measure the trail, wheel and tyre size and keep records. Very minor changes can have a big effect.

L.A.B. said:

swooshdave said:

Frames are the same.

Click to expand...

There's 1.0 degree difference in steering angle between the 750 and 850 frames, supposedly? :?

Click to expand...

In the bare frame or are you including the forks?

I thought the '1 degree was in the 850 triple clamps ?

Time Warp said:

I thought the '1 degree was in the 850 triple clamps ?

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They increased the angle of the steering head in the frame by 1 degree and then pulled back the forks by decreasing the angle of the forks by 1 degree to maintain the same wheelbase.

Time Warp said:

I thought the '1 degree was in the 850 triple clamps ?

Click to expand...

http://www.classicbike.biz/Norton/Repai ... mmando.pdf
Section F, Fig F4

"Frame Checking Data 750 Models"
63 (27) degrees


"Frame Checking Data 850 Models"
62 (28) degrees

And the steering head head angle doesn't change with different triple clamps anyway...

To me this begs the question, does adding stability take away feel and responsiveness.

Click to expand...

Yes, To me its the most deciding undesirable factor to never seek or want to keep an 850 frame/stem set up. A friend stored his '74 in my shed for a number of years while I learned how to rebuild my 1st Combat and then took on getting the 850 going and could feel its ponderous resistive extra work handling compared to Wes's and my 750s just going 100 yd on grass from shed to Gravel driveway and then also on mild hwy travel for no more interest at all to get it at a bargain price. The 850 I was given by Rich Stone to ride 100+ miles back from a Baxter's Cycle rally I'd ridden to on his Combat was about the same as the Combat - as long as I just flowed along with traffic and didn't try passing cars whipping around with any thrill. I was poorly impressed with just the one degree extra forward rake and truly feel sorry for those with 850 models trying for anything but chopper like use. I've ridden long fork springer HD hard tail choppers, parking lots, Mt. Hwy and freeways to have imprinted comparison.
As for top speed handling stability - remember all the fastest most famous Commandos > were not 850 frame and stem angles. My SV650 has ~25' rake and is too damn twitchy to really take on the Mt. twisties w/o its surprise stand up hi sides or skip out low sides nor even have fun on easy pasture, which freaked me out after 100 yd to tippy toes back to terra firma and swore off any Steve McQueen fun with it. My SV650 feels kind of ponderous extra effort to steer and buzzy compared to good ole 750 Commandos to me. I believe that the 850 sluggishness in handling and acceleration to hi speed was as much a reason for Norton's market failure as all the other factors books written on. I can not imagine anyone having a 750 wanting to buy one after a short test ride when they were new in the later '70's.

Interesting dialog. If you ask two people, you get different answers. Ask Norvil and he says 850, ask Norman white and he say 750.

When I went with a 18" rear wheel, one Norton specialist thought I was nuts, saying that the bikes handle better on 19" all around. I see racers with both sizes, but rarely a mixed set front to back.

I
The 850 would be more stable at the speed of light , and the 750 better for moto cross / Enduro use ,
roughly put . The Drawings NOT showing the reinforing gusset to the rear loop from the inner shock mount ,
which is easy to spot as differentiation . But Not All 850 frames had the extended inner gusset , at first .
Mk IIIs have big ugly holey shock top mounts .

Sure , the 750 frames faster steering , WITH Less Rake & Trail . as its read from thew VERTICAL , and tyre contact AFT of Axle from a VERTICAL Line . for the ree cord .

" ok, thanks, its really 28 degrees for the 850 and 27 for the 750 " viewtopic.php?f=1&t=12097&p=140727&start=0&view=show#p140727